For a backlight of a liquid crystal panel used for a mobile phone or others, a white light-emitting LED is used. In order to obtain an evenly-uniformed light emission luminance, it is required to drive the LED under a constant current condition so that a predetermined constant current is flown in the LED.
As a technique relating to this, a specification of U.S. Pat. No. 6,621,235 (Patent Document 1) discloses a technique of uniformly emitting an LED array in which LED devices are connected in multi series and multi parallel. Also, Japanese Patent Application Laid-Open Publication No. 2007-129862 (Patent Document 2) and LM3432 datasheet “LM3432/LM3432B 6-Channel Current Regulator for LED Backlight Application” published by National Semiconductor Corporation on May 22, 2008 (Non-Patent Document 1) disclose a technique of controlling a voltage applied to an LED array in accordance with variation in a forward voltage VF of the LED so that a voltage applied to a constant-current driving device is not unnecessarily increased, and a technique of suppressing “generation of a power control signal with a fault voltage level” and “abnormal operation of an LED short detecting circuit” due to increase of an LED terminal voltage in digitally dimming an LED array.